In the meat industry, and particularly in those areas devoted to the processing of beef and pork, meat packers slaughter animals in a process in which the animals are stunned, bled, skinned, eviscerated, and fabricated into meat sections which are then marketed in grocery stores and in the restaurant trade. Animals enter a meat slaughter plant with various foreign materials present on their hair, including blood, dirt, manure, mud, and vegetative material. An animal's hair is also contaminated with a multitude of microorganisms, some of which are pathogenic to humans. Most bacteria present in a meat slaughtering and processing facility are carried into the facility on the hides of animals to be slaughtered. During the slaughtering process these microorganisms contact meat and other meat by-products, thereby contaminating such products, creating handling problems and reducing the shelf life and safety of the meat products.
The control of contamination by microorganisms is a recognized problem in the meat packing industry. The preparation of food products, and particularly fresh meat and meat products for the retail market, is largely concerned with the control of microbial contact with food in order to increase the shelf life of food products. Food products having an extended shelf life afford more time in which handlers, shippers, and wholesalers can transport and sell such food before spoilage occurs. Efforts to increase the shelf life of food products, such as meat, have traditionally been focused on reducing the number of bacteria present on the surface of the food product.
Freezing food, and particularly meat, has proven to be an effective way in which to retard the growth of bacteria that may be present on the surface of the food. The freezing of meat, however, especially for extended periods of time, has many undesirable effects. By freezing a meat product, water within the meat crystallizes, causing the denaturing of proteins and other damage to the meat on a cellular level. Moreover, the texture, consistency and taste of thawed frozen meat is less desirable than that of fresh meat. Because of the relative short shelf life of fresh meat, foreign markets can only be reached by freezing domestic meat products. Many foreign meat consumers, such as those in the Pacific rim countries and Europe, prefer fresh meat to frozen meat. Such fresh meat preference effectively preclude foreign sales of domestic meat. Without freezing the meat product, however, the bacteria that has contacted the meat during processing are able to proliferate, creating spoilage and pathogenic concerns.
The opportunity for bacterial contact with the fresh meat begins when an animal is initially presented for processing and extends up until the time the meat product is consumed. The initial bacterial contact with fresh meat is encountered with a meat processing facility due to the contaminated state of the animal when it enters the facility. Further opportunities for bacterial contact arise from the significant amount of human handling and equipment exposure during the slaughter, processing, and transportation of meat products. Moreover, when consumers remove the wrapping of a meat product for cooking, additional opportunities present themselves for bacterial infection.
The time between the initial opportunity for bacterial contact with meat products and the ultimate consumption of such products by consumers, allows for the proliferation of various forms of bacteria, including the growth of undesired spoilage and pathogenic bacteria. The growth of undesired bacteria on meat presents aesthetic concerns affecting the marketability of meat products. For example, growth of spoilage bacteria creates undesired odors due to bacterial production of certain esters, hydrogen sulfide, nitrogenous compounds, ruturic acid, propionic acid, formic acid, as well as other undesirable gases and acids. The growth of other such bacteria also acts to discolor the surface of the meat. Moreover, when meat packaged in permeable plastic packages spoils, the packaging often inflates due to the generation of gas produced by spoilage bacteria.
Contamination of meat with pathogenic bacteria is also a great concern since such bacteria, or toxins produced by such bacteria, can cause illness or disease in humans and animals who consume such meat. The shelf life of a meat product is directly related to the number of spoilage and pathogenic bacteria present on the surface of the meat product. A meat product having a high level of spoilage and pathogenic bacteria on its surface exhibits a relatively short shelf life, whereas meat having a low count of spoilage and pathogenic bacteria exhibit an extended shelf life.
There has been a long felt need in the meat packaging industry for controlling undesired bacterial proliferation in order to avoid spoilage and thereby increase the shelf life of meat products. Government standards also mandate that meat processing facilities attain certain tolerances which have been set regarding the number of potentially hazardous bacteria that meat may contain. Methods by which undesired bacterial growth on meat can be controlled are therefore desired.
In a meat processing facility, animals are slaughtered and fabricated in a process which progressively disassembles the animal to produce meat cuts for sale to customers. When an animal to be slaughtered enters a processing facility, it typically has a great variety of bacteria present on its hide. Bacteria present on an animal primarily originate from the foreign material present on an animal's hide, including blood, dirt, manure, mud and vegetative material. The necessary handling of meat products during the fabrication process provides additional opportunities for meat to come into contact with bacteria. In conventional meat processing facilities, it has not been economically feasible to remove all sources of material contact with the meat or to maintain perfect environmental conditions to retard bacterial growth.
The prior art utilizes several methods to prolong the retail acceptability of meat products. For example, vacuum packing of meat in gas permeable packages is commonplace. Irradiation with ultraviolet light has been used to reduce the number of microorganisms on meat surfaces. Salting of meat has long been practiced to preserve meat products. Refrigeration is also widely used to deter the rapid growth of spoilage and pathogenic bacteria on meat products. Spoilage bacteria, such as pseudomonas, are known to grow most rapidly at about room temperature. Although such bacteria are present on meat at lower temperatures, their growth is significantly slowed by cooler environments. Mere refrigeration alone, however, is not totally effective in preventing or adequately retarding the growth of spoilage or pathogenic bacteria for any appreciable amount of time.
The shelf life of meat has also been extended somewhat by the use of chemical agents. Chemical treatment of meat to destroy surface bacteria has traditionally been accomplished by treating meat with weak acids and/or chlorine solutions. These conventional techniques, however, often create undesirable color, flavor and order modifications of meat, and are often ineffective to maintain meat in a saleable condition for any appreciable period of time.
Although the control of spoilage and pathogenic bacterial growth is a recognized problem in the meat packing industry, the reduction of meat shelf life attendant to such growth continues to be a significant problem. Many techniques have been employed in the past in an effort to destroy surface bacterial flora on meat. For example, U.S. Pat. No. 4,852,216 to Clayton discloses a disinfection system using an acetic acid spray in order to reduce bacterial levels and thereby increase shelf life of meat products. Similarly, U.S. Pat. No. 3,924,044 to Busch discloses a method for applying a hot, dilute acid solution to meat surfaces to destroy psychotropic spoilage bacteria on meat surfaces. U.S. Pat. No. 3,991,218 teaches the encapsulation of meat products in a film of alginate material to retard the growth of anaerobic bacteria on the surface of the meat. Other inventors have utilized anti-microbial agents for preserving products normally subject to microbial spoilage. For example, U.S. Pat. No. 3,915,889 to Jurd discloses a certain anti-microbial agent that can be applied for preservation for a wide variety of substances including meat.
Other inventors have recognized the advantages of dehairing animals to facilitate the slaughtering process. U.S. Pat. No. 4,674,152 to Georges discloses an apparatus and method for slaughtering animals by bleeding an animal, electrostatically charging the animal's hair, applying a combustible fluid to the hair and subsequently igniting the combustible fluid to burn the hair from the animal's body. U.S. Pat. No. 4,309,795 to Simonsen discloses a method and apparatus for de-hairing hogs wherein the hog is bled, its skin is scalded with hot water, and then subjected to abrasive treatment to remove the hogs hair.
In a direct teaching away from the present invention, other researchers have concluded that contacting meat products with lactic acid bacteria, and thereafter vacuum packaging such meat in impermeable plastic, is ineffective in controlling the growth of pathogenic and spoilage bacteria on the meat. For example, the companion articles by Hanna et al., "Inoculation of Beef Steaks with Lactobacillus Before Vacuum Packaging, I. Microbiological Considerations," Journal of Food Protection, Vol. 43, pp. 837-841 (November 1980) and Smith, G. C. et al., "Inoculation of Beef Steaks with Lactobacillus Species Before Vacuum Packaging. II. Effect on Meat Quality Characteristics," Journal of Food Protection, Vol. 43, pp. 842-849 (November 1980) disclose that disadvantages outweigh advantages for inoculation of beef with Lactobacillus cultures prior to vacuum packaging of meat. In addition, Egan et al., "Significance of Lactobacilli and Film Permeability in the Spoilage of Vacuum-Packaged beef," Journal of Food Science, Vol. 47, pp. 119-126 (1982) disclose that even in the absence of a significant population of contaminating microorganisms, sterile vacuum packaged beef has a limited shelf life and the addition of Lactobacillus bacteria to vacuum packaged meat increases the rate of spoilage. Therefore, no prior art techniques have taught the effective elimination of growth of undesired bacteria to achieve a significant extension of shelf life in fresh meat products.
In the meat packing industry, many types of bacteria are known to cause food poisoning including: E. coli, Salmonella, F. coliforms, Listeria, Staphylococcus, F. streptococcus, Bacillus anthraces, Balantidium coli, Campylobacter coli, Campylobacter jejune, Francisella tularensis, Sarcocystis, Taenia saginata, Taenia solium, Toxoplasma gondil, Trichinella spiralis, Yersinia enterocolinea, Yersinia pseudotuberculosis, Brucella, Chlamydia petechia, Leptospira and Clostridium. These pathogenic bacteria each group and proliferate under different conditions, any or all of which may be present in a meat processing facility. For example, Listeria is generally found in cool, damp environments such as coolers and meat processing areas. Staphylococcus is often found on cattle hair, in fecal material, in infected cuts and internal abscesses, and is sometimes associated with poor hygienic practices of food handlers.
Spoilage bacteria, including psychotropic bacteria such as Pseudomonades, Lactobacillus and Coliform, affect the shelf life of meat products by causing discoloration of meat and undesired odors. These bacteria are typically found in soil, ingesta, and fecal material that are commonplace on an animal's hide.
The bacteria present on an animal's hide can be roughly divided into three distinct categories: pathogenic bacteria, lactic bacteria, and spoilage bacteria. In the environment of a meat processing facility, spoilage bacteria typically proliferate at a greater rate than do pathogenic bacteria or lactic bacteria. It has been recognized that various sanitizing techniques, including acetic acid sprays, application of anti-microbial agents, and irradiation, can be used to reduce the total number of bacteria present on an animal carcass. However, while the total number of bacteria can be reduced, it is difficult to specifically kill pathogenic and spoilage bacteria without eliminating all the bacteria present on an animal carcass.
Additional difficulties are experienced in the control of certain types of bacteria, namely Salmonella and Listeria, which initially infect meat by implanting themselves on meat surfaces. After contact, such bacteria immediately initiate the secretion of a waxy material to protect themselves from the outside environment. Unless these bacteria are contacted with chemical agents, such as acetic acid, before significant implantation and secretion of waxy substances, such bacteria are extremely difficult to remove from the meat.
Conventional wisdom in the meat processing industry teaches the maintenance of low bacterial counts as measured by the total number of bacteria on a meat product. For example, if bacterial counts exceed about ten million bacteria per gram of meat, the meat is disposed of as a matter of course. However, a total bacterial count includes not only the number of pathogenic and spoilage bacteria, but also non-pathogenic, non-spoilage bacteria.
In view of the above, a need exists for a method for preserving food products, particularly fresh meat and meat by-products, by selectively reducing the number of spoilage and pathogenic bacteria present on such food products.